Variable inductance tuning



y 1 D. E. FOSTER 2,375,911

VARIABLE INDUCTANCE TUNING I Filed July '16, 1942 jivsmdrlolv For/n5aft/44470,?- C014 iNVENTOR gems) Fosr'm,

j y ATZTORNEY' I Patented May 15, 1945 VARIABLE INDUCTANCE TUNING DudleyE. Foster, Toronto, Ontario, Canada, assignor to Radio Corporation ofAmerica, a corporation of Delaware Application July 16, 1942, Serial N0. 451,095

6 Claims.

, My present invention relates to so-called permeability tuners forradio receivers.

One of the objects of my invention is to provide a heterodyne circuitwherein the oscillator and converter circuits utilize iron core tuners;the coils of the two circuits being concentrically wound with respect toa single, common adjustable iron core.

Another object of the invention is to provide an oscillator-converternetwork wherein the oscillator and converter coils are concentricallywound, and a single core of comminuted magnetic particles is used forconcurrently adjusting the inductance of said coils.

Another object is to provide a multi-range receiver wherein the coils ofthe tuned circuits of the different ranges are adapted to be varied ininductance by a single adjustable iron core.

Yet another object of my invention is to provide a multi-range receiverwherein inductance tuning is employed, and asingle iron core elementbeing employed to vary the inductance in either tuning range,

Still other objects are to improve generally the simplicity ofpermeability tuners, and more especially to provide multi-rangeinductance tuners which use a single core element for economy ofconstruction,

The novel features which I believe to be characteristic of my inventionare set forth in particularity in the appended claims; the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin connection with the drawing in which I have indicateddiagrammatically several circuit organizations whereby my invention maybe carried into effect.

In the drawing:

Fig. 1 shows an embodiment of the invention applied to anoscillator-converter network; the tuner being shown in section,

Fig. 2 shows the invention applied to a multirange receiver,

Fig. 2a shows the tuner of Fig. 2 applied to an amplifier,

Fig. 3 shows a modified multi-range tuner construction, and

Fig. 3a shows the circuit connections for the tuner elements of Fig. 3.

Referring, now, to the accompanying drawing, wherein like referencecharacters in the figures designate similar circuit elements, thenumeral I denotes the oscillator circuit coil of a heterodyne receiver.The coil I is wound on aninsulation form 2. The form is cylindrical, andthe coil I is wound in the usual manner. The condenser 3 shunts coil I,and is chosen in magnitude so that proper variation of the inductance ofcoil I will result in a variable tuning range of the desired frequencycoverage. The cylindrical insulation form 4 has the coil 5 wound alongthe external surface thereof. The condenser 6 shunts coil 5.

- The coil 5 and condenser 6 provide the converter,

or first detector, tunable input circuit. The manner of keeping theforms spaced is well known to those skilled in the art.

The numeral 1 designates an iron core element which is axially locatedrelative to form 4. Core 1 is preferably composed of comminutedparticles of magnetic material, such as iron, bound together by any wellknown insulating adhesive binder. Reciprocation of the core 1 within theconcentric coils l and 5 results in concurrent variation of theinductances thereof. My invention is specifically intended for asuperheterodyne receiver wherein the resonant circuit 56 is locatedbetween the input electrodes of the converter tube, and the circuit l-3is the tunable tank circuit of the local oscillator. One orimore radiofrequency amplifiers may feed the tuned circuit 5-6.

The local oscillations are fed to the first detector tube; theintermediate frequency (I. F.) energy is produced in the plate circuitof the first detector. Assume, by way of specific illustration, that thefrequency range of circuit 5-6 is desired to be 550 to 1700 kilocycles;this is the standard amplitude modulation broadcast band in thiscountry. The oscillator frequency is usually operated over a higherfrequency range, and differs by the I. P. value. Assume the I. F. valueto be 465 kilocycles (kc.) Then, the oscillator circuit will be tunableover a range of 1015 to 2165 kc.

The oscillator and converter resonant circuits l3 and 5t are eachadjusted over the respective frequency ranges by movement'of the common,compressed comminuted ferromagnetic core 1 relative to the inductancecoils l and 5. This is so-called permeability tuning. In the past it wasdeemed necessary to use a separate adjustable core for each resonantcircuit. The change in permeability, hence inductance and frequency, isa function of the ratio of winding diameter to core diameter. In asuperheterodyne receiver, with the local oscillator frequency higherthan signal frequency, the ratio of maximum to minimum frequnecy over agiven band is less for the oscillator than for the signal frequency.

The signal frequency ratio is fmux. fmln.

whereas the oscillator frequency ratio is .frnux. fmin.

According to my invention the oscillator coil I is located externally ofthe converter coil 5. The diameter of coil I is substantially greaterthan the diameter of coil 5. Further, the oscil lator coil turns arespaced at greater intervals than the converter coil turns. The diametersof the coils l and 5 are so chosen that the common core I mayconcurrently vary the signal frequency tuning from fmax. to fmin, whilethe oscillator frequency is varied from fmux. +1. F. to finiu.+ I. F.Reference is made to Measurement of iron cores at radio freqencies(Equations 6 and 7) by D. E. Foster and A, E. Newlon (I. R. E. May,1941, page 266) for the required ratio of diameters. The core 1 is to besufficiently long to be able to nest within the form 4 at one endposition, and be entirely outside the form 4 at the opposite frequnecylimit. When core 1 is completely withdrawn, then both circuits are tunedto maximum frequencies.

In Fig. 2 I have shown another use to which the present invention can beput. In the case of multi-range receivers it is necessary to switch theinput electrodes of an amplifier from one tuned circuit operating in onefrequency range to another tuned circuit operating in a differentfrequency range. .For example, considering Fig. 2a, the amplifier 8 is aradio frequency amplifier of the usual type. For short wave reception itis provided with a resonant circuit 9 which consists of a coil I0shunted by condenser I I. For broadcast reception there is provided adifferent resonant circuit l2 which consists of a coil l3 shunted bycondenser l4. The switch I5 is arranged to connect either of the tworesonant circuits in electrical circuit with the input electrodes ofamplifier 8, depending on the frequency band in which the multi-rangereceiver is operating. Each of the resonant circuits 9 and I2 is of thepermeability tuning type. A common iron core I6 is employed for tuningeither of the circuits 9 or IE. In the prior art each resonant circuitused its own iron core tuning element.

In Fig. 2 there is shown the specific manner of constructing the tuningmechanism. The short wave coil I0 is wound on an insulation form H).

In axial alignment therewith there is provided a I second insulationform i3 upon which is wound the coil l3. The iron core i5 has secured toit a mechanism I! which may reciprocate the iron core within theinsulation forms 13 and it, An electrostatic shield 20 is providedintermediate the coils I3 and ill so as to shield them from each other.It will, of course, be understood that in actual practice there will besufficient physical spacebetween the insulation forms [3' and IE3 topermit the iron core Hi to be entirely withdrawn from form it withoutentering into form Ill.

It will, therefore, be seen that in Fig. 2 the same iron core I5 is usedto tune through two different frequency bands with the same travel. Theshield 21} prevents coupling between the coils even though one is not inuse; this is the prevention of dead-end effect. In Fig. 2 the directionof core motion which decreases inductance in the broadcast band willincrease inductance in the short wave band and vice versa. Of course, byincreasing the travel of the core added frequency bands may be used ateither end of the core travel.

In Fig. 3 I have shown a further modification of the manner of using thesame core for two or more frequency bands. In this case the short wavecoil It is wound concentrically with the broadcast band coil 13. Ofcourse, the insulation form ii! is concentric with the insulation form3. The core it is reciprocable within insulation form 63. Of course,only one of the concentric coils will be effective during motion of thecore it. As shown in Fig. 3a, the inductance of coil H) is thrown inparallel with that of coil 43 for operation in the short wave band. Theinductance coil 13 of the broadcast band is assumed to have a highinductance. The inductance of the short wave band is determined main- 1yby coil It. The dead-end effect of the coil 13 on coil ii) is avoided bythe parallel connection of the two coils. Only a single condenser 20need be used for either of the bands. The switch 2| when open permitstuning by core H5 in the lower frequency band. When closed, tuning isaccomplished in the higher frequency band. Here, again, the aforesaidarticle is referred to for data on design of the coils.

While I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention, as set forth in the appendedclaims,

What I claim is:

1. In combination, an oscillator network comprising a coil shunted by acondenser and adapted to be tuned over a range of frequencies, aconverter network comprising a second coil shunted by a second condenserand adapted to be tuned over a different range of frequencies, saidcoils being disposed in concentric relation, and a single ferromagneticcore movable within said coils to concurrently vary the inductances ofsaid coils to thereby adjust the tuning of both networks.

2. In combination, a permeability tuner for a superheteroclyne receiver,said tuner comprising a first coil included in the oscillator network, asecond coil of less diameter than the first coil concentrically disposedrelative t the latter and included in the converter network, and asingle ferromagnetic core movable axially with respect to said coils forsimultaneously adjusting the tuning of said oscillator and converternetworks.

3. A tuning system for a superheterodyne receiver comprising a pair ofcircuits which are tunable through frequency ranges of different widths,a variable permeability-tuned inductance included in the circuit that istunable through the Wider frequency range, a second variablepermeability-tuned inductance included in the circult that is tunablethrough the narrower frequency range, said inductances being in the formof coils disposed in concentric relation, and a single ferromagneticcore movable within said inductance coils-for effecting the simultaneousadjustment thereof in the tuning of said circuits through theirrespective frequency ranges.

i. A tuning system for a superheterodyne receiver comprising a signalfrequency circuit and an oscillator circuit, a variablepermeabilitytuned inductance included in the signal frequency circuit, asecond variable permeabilitytuned inductance included in the oscillatorcircuit, said inductances being in the form of coils disposed inconcentric relation, and a single ferromagnetic core movable relativelyt said inductance coils for effecting the simultaneous adjustmentthereof in the tuning of said circuits through their respectivefrequency ranges.

5. A tuning system for a superheterodyne receiver comprising a pair ofcircuits which are tunable through frequency ranges of different widths,a, variable permeability-tuned inductance of predetermined winding pitchand diameter included in the circuit that is tunable through the widerfrequency range, second variable permeability-tuned inductance ofgreater winding pitch and diameter than the first inductance included inthe circuit that is tunable through the narrower frequency range, thetwo inductances being disposed in concentric relation, and a singleferromagnetic core movable coaxially within said inductances foreffecting the simultaneous ad justment thereof in the tuning of saidcircuits through their respective frequency ranges.

6. A tuning system for a superheterodyne receiver comprising a signalfrequency circuit and an oscillator circuit, a variablepermeabilitytuned inductance of predetermined winding pitch and diameterincluded in the signal frequency circuit, a second variablepermeability-tuned inductance of greater winding pitch and diameter thanthe first inductance included in the oscillator circuit, the twoinductances being disposed in concentric relation, and a singleferromagnetic core movable coaxially within said inductances foreffecting the simultaneous adjustment thereof in the tuning of saidcircuits through their respective frequency ranges.

DUDLEY E. FOSTER.

